Catalysts and process for unsaturated aldehydes

ABSTRACT

A catalyst composition useful for the oxidation of olefins, particularly the vapor phase oxidation of isobutylene and/or tertiary butyl alcohol to produce methacrolein, consists essentially of the combination of oxides of molybdenum, cobalt, iron, bismuth, thallium, antimony, silicon, and nickel, along with one or more members of the groups consisting of the alkali metals, the alkaline earth metals, the rare earth metals including lanthanum, tungsten, and mixtures thereof. The catalyst has a BET surface area within the range of about 0.5-10 m 2  /gm and preferably within the range of about 2-6 m 2  /gm. Preferably, the catalyst has no more than about 3% of the surface area associated with pores smaller than about 100 A°. The catalyst is heated during its preparation to a temperature above 525° C., preferably above 550° C., most preferably to about 600° C., for a time sufficient to achieve the desired surface area and pore size distribution and thereby to improve selectivity to methacrolein.

This is a continuation, of application Ser. No. 939,645 filed Sept. 5,1978, now abandoned.

PRIOR ART

This invention relates to catalysts, and is more particularly concernedwith catalysts for the vapor-phase oxidation with molecular oxygen ofisobutylene and/or tertiary butyl alcohol to produce methacrolein and toa process for using such catalysts.

It is well known that unsaturated aldehydes, such as acrolein andmethacrolein, can be produced by the vapor-phase oxidation of thecorresponding olefins by means of molecular oxygen in the presence of asuitable oxidation catalyst. A variety of catalyst compositions havebeen proposed for this purpose and many such compositions comprise theoxides of molybdenum, iron, and bismuth in particular. As a generalrule, however, the selectivity to the desired aldehyde, i.e., the molarquantity of aldehyde obtained per mol of olefin converted, has beenrelatively low when catalyst compositions of this type have beenemployed. More recently, attempts have been made to increase theselectivity of the reaction by incorporating oxides of more unusualelements in the catalyst.

In U.S. Pat. No. 4,087,382, an improved catalyst is disclosed whichincludes the elements molybdenum, bismuth, iron, cobalt, thallium,antimony, and optionally silicon. Such catalysts have been found to haveimproved performance over catalysts of the prior art. However, furtherimprovements were still sought since, when such catalysts are operatedat above-atmosphere pressures, as is typical of commercial practice,inferior results are obtained compared to the performance at atmosphericpressure. Regaining the lost performance at above-atmospheric pressurewas desirable for a commercially viable catalyst. In addition, animprovement in the long-term stability of the catalyst was desired.

The present invention comprises an improved catalyst of similarcomposition to that of the commonly assigned U.S. Pat. No. 4,087,382,but with additional elements which have been found to improve theperformance, as will be seen in the discussion hereinafter.

The description of the prior art related to catalysts for use in theoxidation of lower olefins to unsaturated aldehydes is difficult in viewof the large number of elements which have been found by variousresearchers to be useful. With regard to the catalyst composition to bedisclosed hereinafter, the following U.S. patents are believed to beparticularly material.

U.S. Pat. No. 4,034,008 to Kurtz, et al. discloses a catalyst which ispotassium free and which contains molybdenum, bismuth, iron, cobaltand/or nickel, antimony and/or ruthenium, and optionally, a trace ofchloride. The patented catalyst does not contain thallium, the rareearth metals, the alkali metals, the alkaline earth metals, or tungsten.Although disclosed broadly for oxidation of alpha, beta-unsaturatedmonolefins to the corresponding aldehydes or carboxylic acids or forammoxidation of the same olefins to the corresponding nitriles, theworking examples only disclose the oxidation of propylene to acrolein.It should be noted that, although propylene and isobutylene arechemically related, the oxidation of isobutylene (or its equivalent,tertiary butyl alcohol) is considered the more difficult reaction tocarry out. Although the catalysts are disclosed to be calcined at400°-550° C. for 2 to 24 hours, the working examples show the catalyststo be calcined at temperatures in the range of 450°-490° C. Also, thecatalysts are disclosed to be preferably disposed on a support such assilica, alumina, silicon carbide, zirconia, and titania.

The significance of the use of thallium is indicated in U.S. Pat. No.3,951,861, Shiraishi, et al., wherein the criticality of the thalliumcontent is shown with relation to a catalyst composition of molybdenum,bismuth, iron, cobalt and/or magnesium and/or manganese, along withnickel, and optionally, phosphorus and a group of other metals,specifically, copper, calcium, strontium, zinc, cadmium, tin and lead.The patentee's catalyst does not contain antimony, the alkali metals, orthe rare earth metals. The patent is directed specifically to theoxidation of propylene to acrolein, although a related patent, U.S. Pat.No. 3,928,462, discloses the benefits of small amounts of thallium in asimilar catalyst used for the oxidation of isobutylene to methacrolein.The catalysts are generally calcined at temperatures in the range of525°-550° C. Preferably, they are disposed on a support such as silica,alumina, silicon, carbide, and titania.

Nickel is used in a number of catalysts, in particular the '861 and '008patents previously mentioned. In U.S. Pat. No. 3,454,630, Yamaguchi, etal., emphasize the benefits of nickel and/or cobalt oxides. Thepatentees consider nickel and cobalt as equivalents, and suggest thatone or the other may be used. The catalyst of the '630 patent lacks thethallium, antimony, silicon, and alkali metals of the instant catalystand requires the presence of phosphorus. Example 41 of the '630 patentabove shows relatively poor catalytic performance with respect to theselectivity to methacrolein.

Silicon has also been indicated to be a useful component of suchcatalysts as indicated in the '008 patent previously mentioned, alongwith U.S. Pat. No. 3,186,955 and U.S. Pat. No. 3,855,308. The catalystof the '955 patent preferably contains barium and more bismuth thanmolybdenum and lacks the iron, cobalt, thallium, antimony, nickel, andalkali metals of the instant catalyst. The catalyst is disclosed formultiple purposes, including the oxidation of isobutylene tomethacrolein. Calcination above about 565° C. was indicated to bedetrimental to the catalyst performance. The catalyst of the '308 patentlacks antimony and nickel, but requires tungsten and is said to becalcined at a temperature between 350°-600° C., although a temperatureof 450° C. was used generally in the working examples.

In British Pat. No. 1,456,752 a catalyst basically consisting ofmolybdenum, bismuth, cobalt, and iron was disclosed to be improved bythe addition of antimony. The patent teaches that antimony has theeffect of improving the selectivity to methacrolein, but lowers activityof the catalyst when it is calcined at temperatures in the range of500°-550° C. In such a situation, the patentees would add at least oneelement from a large group of elements including barium and nickel inorder to restore the activity lost by adding antimony. The patenteesfurther disclose that if a catalyst is calcined between a temperature of600°-700° C., improved activity was obtained. To such catalysts, theywould add an alkali metal and/or thallium. In the example, the catalystswere generally mixed with silicon carbide powder as a carrier. Thepatent states that pressure was not critical in the reaction. The patentcontains no information with regard to the surface area or the porediameter of the catalyst disclosed. Silica is not included as aningredient of the catalyst.

In general, it is believed that the composition of a catalyst of thistype cannot be predicted merely by combining the many elements whichhave been disclosed in the prior art, but that the catalyst performancemust be determined experimentally at the expected operating conditions.Consequently, small changes in composition may be very important inachieving improved catalyst performance and particularly in optimizingthe catalyst composition to suit a specific reaction and set ofoperating conditions.

As will be shown in the description of the invention which follows,changes in operating conditions and in methods of preparation may resultin a degradation of catalyst performance and make if necessary to addingredients to a catalyst in order to recover the loss in performance.

SUMMARY OF THE INVENTION

It has been discovered that the conversion of isobutylene and/ortertiary butyl alcohol with high selectivity to methacrolein can beaccomplished by carrying out the vapor-phase molecular oxidation in thepresence of a catalyst composition which consists essentially of theoxides of molybdenum, cobalt, iron, bismuth, thallium, antimony,silicon, nickel, and one or more members of the group consisting of thealkali metals, the alkaline earth metals, the rare earth metalsincluding lanthanum, tungsten, and mixtures thereof.

The catalyst composition of the invention may be expressed by thefollowing general formula:

    Mo.sub.a Co.sub.b Fe.sub.c Bi.sub.d Tl.sub.e Sb.sub.f Si.sub.g Ni.sub.h X.sub.i O.sub.j

wherein X is at least one member of the group consisting of the alkalimetals, the alkaline earth metals, the rare earth metals includinglanthanum, tungsten, and mixtures thereof and where a to j indicate theatomic ratio of each component so that where a is 12, b is 0.2-8, c is0.05-5, d is 0.2-4, e is 0.01-5, f is 0.01-5, g is 1-20, h is 0.05-5, iis a positive value up to 4, and j has a value which is determined bythe valence and proportions of the other elements in the catalyst.

More specifically, a preferred catalyst composition according to theinvention comprises the oxides of the specified elements in thefollowing atomic ratios: Mo=12, Co=4, Fe=3, Bi=1, Tl=0.5, Sb=0.3,Si=6.6, Ni=2, Cs=0.3, and K=0.3, based on the composition of theoriginal solutions. The catalyst composition may be regarded either as amixture of oxides of the named elements or as oxygen-containingcompounds of the elements and the use of the phrase "mixture of oxides"shall be understood to include either or both forms. As prepared and/orunder the reaction conditions, the catalyst may contain either or bothforms.

The catalyst is prepared by methods generally known in the art, but iscalcined at higher temperatures than those generally employedheretofore, namely, at least above 525° C. and preferably above 550° C.After calcination for a sufficient period of time, the catalyst of theinvention will have a BET surface area within the range of about 0.5-10m² /gm, preferably within the range of about 2-6 m² /gm and will have nomore than about 10% of the pore volume, preferably about 3%, associatedwith pores smaller than about 100 A°.

In another aspect, the invention includes a process for the vapor-phaseoxidation of isobutylene and/or tertiary butyl alcohol to producemethacrolein in the presence of the catalyst described above.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Catalyst Composition andPreparation

The catalyst of the invention consists essentially of the oxides ofmolybdenum, cobalt, iron, bismuth, thallium, antimony, silicon, nickeland one or more members of the groups consisting of the alkali metals,the alkaline earth metals, the rare earth metals including lanthanum,tungsten, and mixtures thereof and having the following general formula:

    Mo.sub.a Co.sub.b Fe.sub.c Bi.sub.d Tl.sub.e Sb.sub.f Si.sub.g Ni.sub.h X.sub.i O.sub.j

wherein X is at least one member of the group consisting of the alkalimetals, the alkaline earth metals, the rare earth metals, lanthanum,tungsten, and mixtures thereof and where a to j indicate the atomicratio of each component so that where a is 12, b is 0.2-8, c is 0.05-5,d is 0.2-4, e is 0.01-5, f is 0.01-5, g is 1-20, h is 0.05-5, i is apositive value up to 4, and j has a value which is determined by thevalence and proportions of the other elements in the catalyst.

The catalyst composition is calcined at a temperature of at least 525°C. for a period of time sufficient to reduce the BET surface area tobetween about 0.5 to about 10 m² /gm of catalyst. Preferably the BETsurface area will be between about 2 and about 6 m² /gm of catalyst andno more than about 3% of the surface will be associated with poreshaving a diameter smaller than 100 A°. The BET surface area is measuredby the nitrogen adsorption method described by Brunauer, Emmett, andTeller in the "Journal of the American Chemical Society", Vol 60, page309 (1938). The pore diameter and volume are determined by the mercuryporosimeter method described by Drake and Ritter in "The AnalyticalEdition of Industrial Engineering Chemistry", Vol 17, page 787 (1945).The surface area, pore size, and pore volume are frequently interrelatedby the equation given by Emmett and DeWitt in "The Analytical Edition ofIndustrial Engineering Chemistry", Vol 13, page 28 (1941).

The catalyst composition is preferably used in the form of pellets orother like compressed shapes of various sizes. The composition may beformed in conventional manner using techniques well known to personsskilled in the art. For example, compounds of molybdenum, cobalt, iron,thallium, antimony, bismuth, cesium, potassium and nickel are eachdissolved in a small amount of water or other solvent, and the solutionsare then combined with colloidal silica and the mixture evaporated todryness. To prepare the catalyst, the several components can beintroduced into the solution in the form of various salts or othercompounds of convenient types and no specific form for the catalystprecursors is necessary. The use of ammonium salts, halides, e.g.chlorides, nitrates, or acid forms of the elements to be supplied are,however, particularly suitable. Preferably, however, aqueous solutionsare employed and water-soluble forms of the elements are used, exceptthat the silica portion of the catalyst is normally insoluble. In somecases, the solutions may have acids and/or bases added to them tofacilitate dissolution of the catalyst precursors. For example, acidssuch as hydrochloric or nitric or bases such as ammonium hydroxide canbe used if desired. Silicon may be added in the form of an aqueouscolloidal solution of SiO₂. Typical suspensions of colloidal silicaparticles in water or alcohol are available from Nalco Chemical Company(Nalcoag®), and E. I. DuPont de Nemours (Ludox®). Colloidal silica isalso available in powder form from Degussa (Aerosil®). The particles mayrange from about 600 A° size which have a BET surface area of 50² m/gm,to particles of 40 A° size, which have a BET surface area of 750 m² /gm.

The powder resulting after evaporation is thoroughly dried andpreferably screened to eliminate large particles which would hinderformation of uniform compressed shapes, such as pellets. Typically, thepowder is passed through a 20-mesh (Tyler) screen. The powder is thenmixed with an organic binder of any conventional type, such as polyvinylalcohol, and the mixture is thoroughly dried and again screened,typically to provide 20-80 mesh (Tyler) size particles. The driedparticles are then preferably combined with a lubricant, again of anyconventional type, such as stearic acid or graphite, and compressed intothe desired shape, e.g. pelletized, or extruded or otherwise shaped, thecompressed shapes typically having heights and diameters of 1/16 inch to3/8 inch. Finally, the thus-produced catalyst composition is activatedat a higher temperature than has generally been used for prior artcatalysts and for a prolonged period as required to obtain the desiredBET surface area. For example and typically, the pellets are placed inan oven or kiln, or in a tube through which air is passed, at anelevated temperature (e.g. at least 525° C., preferably above 550° C.)for two to ten hours. In a particularly preferred activation step, thetemperature is raised at the rate of 20° C. per hour to 600° C. and thistemperature is maintained for 3 hours.

It will be understood that the foregoing description regardingpreparation of the catalyst in a form suitable for use in a vapor-phaseoxidation reaction is merely illustrative of many possible preparativemethods and is given solely by way of exemplification, except that thecalcination portion of the preparation procedure is an important aspectof the present invention. This method is, however, particularly suitableand is preferred.

USE OF THE CATALYST

The catalyst and the processes of the present invention are usefulgenerally for the production of unsaturated aldehydes by oxidation withmolecular oxygen of lower olefins and the ammoxidation of olefins. Thepreferred starting materials are the monoethylenically unsaturatedolefins having 3 or 4 carbon atoms, or mixtures of olefins. Aspreviously noted, catalysts are specifically developed for optimumperformance with particular feed stock and operating conditions. Thus,the catalyst disclosed and claimed herein is especially suited to theoxidation of isobutylene and/or tertiary butyl alcohol to methacrolein.

When the catalyst of this invention is used in the vapor-phase oxidationof isobutylene and/or tertiary butyl alcohol to form methacrolein, theoperating conditions employed are those generally associated with thisreaction. Thus, the reaction in which the catalyst compositions of thisinvention are of particular utility and in which they provide highselectivity involves contacting isobutylene and/or tertiary butylalcohol in the vapor phase with the catalyst and molecular oxygen,preferably also in the presence of steam. Once reaction is begun, it isself-sustaining because of its exothermic nature. A variety of reactorswill be found to be useful and the common multiple tube heat exchangertype in which the catalyst pellets are disposed inside the tubes issatisfactory. The process can be carried out in conventional equipmentcommonly employed for reactions of this type.

The gaseous feed to the reactor contains relatively low concentrationsof olefin, oxygen and steam. Typically, an inert gas, such as nitrogen,is also present. The oxygen is usually added as such, or as air, or asair enriched with oxygen. As mentioned, conventional oxidationconditions can be employed but, for best results, the olefin isgenerally present in concentrations of about 2 to 20 volume percent ofthe total feed with a preferred range of about 5 to 15 volume percent,and the corresponding ranges for oxygen are 4 to 30 volume percent (aslimited by the flammable range of mixtures) and preferably 10-20 volumepercent and for steam up to 30 volume percent, and preferably 5 to 25volume percent, the balance being the inert gas or gases.

The temperature of the reaction should, for best results, be within therange of from about 250° to 500° C., preferably 300° to 400° C., and theoptimum temperature range is 310° to 370° C. Because the reaction isexothermic, means for conducting the heat away are normally employed,such as by surrounding tubes containing catalyst pellets with a saltbath or with boiling water.

The pressure in the reactor has an effect on the catalyst performance aswill be seen later. While the reaction may be conducted at atmospheric,superatmospheric, or subatmospheric pressure, preferably pressuresranging from atmospheric up to 15.1 kg/cm² absolute, preferably up to 8kg/cm² absolute, and most preferably up to 6.3 kg/cm² absolute areemployed. Typically, a pressure of about 3.4 kg/cm² absolute is used.

The methacrolein product may be recovered by various methods known tothose skilled in the art. For example, the methacrolein may becondensed, or scrubbed with water or other suitable solvents, followedby separation of the unsaturated aldehyde product from the scrubbingliquid. The gases remaining after the methacrolein-removal step may berecycled to the reaction, if desired, and in such case the net CO₂produced by the reaction may be removed by conventional means, such asabsorption in an aqueous carbonate solution, or purged from the system.

The features of the invention will be more readily apparent from thefollowing specific examples. It will be understood, however, that theseexamples are for the purpose of illustration only and are not to beinterpreted as limiting the invention.

EXAMPLE 1 Prior Art

In 750 cc of water are dissolved 636 grams of the molybdenum salt (NH₄)₆Mo₇ O₂₄.4H₂ O. Then 262 grams of Co(NO₃)₂.6H₂ O are dissolved in 300 ccof water, 60.6 grams of Fe(NO₃)₃.9H₂ O are dissolved in 200 cc of water,79.8 grams Tl NO₃ are dissolved in 400 cc of water, 68.4 grams of Sb Cl₃are dissolved in a mixture of 100 cc of water, and 30 cc of concentratedHCl, and 275 grams of Bi(NO₃)₃.5H₂ O are dissolved in a mixture of 200cc of water and 50 cc of concentrated nitric acid. Sufficient ammoniumhydroxide is added to bring the pH of the solution to a value of 7.These solutions are fed to a rotary dryer of 4000 cc capacity and themixture in the dryer is evaporated to dryness and the temperature raisedto 300° C. The resulting powder is removed from the dryer and dried inan oven at 400° C. for 12 hours. The dried powder is screened through a20-mesh screen, a 4% aqueous solution of polyvinyl alcohol is added insufficient quantity to make a damp mixture and this mixture is dried at75°-80° C. until the moisture content reaches 2-4%. The dried mixture isthen screened to 20-60 mesh, and about 2% of stearic acid powder isthoroughly mixed with it. The resulting mixture is then pelletized toform pellets of 3/16 inch height and diameter. The pellets are thenactivated in an oven by heating them gradually at a rate of 20° C. perhour to about 380° C. and maintaining them at this temperature for 16hours. The activated pellets have a density of 0.95 gm/cc, a surfacearea of 6.5 m² /cm. The catalyst components molybdenum, cobalt, iron,thallium, antimony, and bismuth, based on the amounts in the originalsolutions, are in the atomic ratios of 12, 3, 0.5, 1, 1, and 1.5,respectively.

A 50 cc quantity of this catalyst composition is placed in a reactordefined by a 1/2"×108" stainless steel pipe, the reactor pipe beingfilled with 300 cc of inert filler (silicon carbide) below the catalystbed and sufficient inert filler above the catalyst bed to fill thereactor. Nitrogen-diluted mixtures containing 9 vol % isobutylene, 10vol % oxygen, and 20 vol % steam are fed to the reactor at a pressureabout one atmosphere, at temperatures ranging from 360°-370° C. and at aspace velocity of about 3000 hr⁻¹. The term "space velocity" is used inits conventional sense to mean liters of gas (Standard Temperature andpressure) per liter of catalyst per hour. The reaction is run withcontinuous introduction of feed and continuous withdrawal of exit gas.The exit gas is analyzed at intervals of several hours by means of gaschromatography except for measurement of CO/CO₂ by infra-red absorption,using conventional techniques. The combined production of methacroleinand methacrylic acid is reported since both products are useful and, ingeneral, the methacrolein will be separated and oxidized in a separatereactor to form additional methacrylic acid, typically for conversion tomethyl methacrylate. The predominant product is methacrolein and theamount of methacrylic acid present is only about 2-3% of the total shownbelow. The experimental results are reported in Table I.

                  TABLE I                                                         ______________________________________                                                       Selectivity, %                                                               Isobutylene                                                                              Methacrolein +                                       Test  Time,   Conversion,                                                                              Methacrylic                                                                             Acetic                                                                              CO +                                 No.   hr.     %          Acid      Acid  CO.sub.2                             ______________________________________                                        1      12     55.0       86.9      2.4   4.7                                  2      62     54.0       88.5      1.7   4.8                                  3     172     61.8       86.8      1.54  4.34                                 4     177     60.0       87.8      1.76  3.70                                 5     180     59.2       87.4      1.9   3.80                                 6     210     61.6       86.0      1.51  4.80                                 7     214     65.3       87.4      1.35  3.91                                 8     231     67.3       88.8      1.85  2.47                                 9     235     59.1       87.5      1.65  3.32                                 10    238     58.6       87.4      1.42  3.65                                 11    255     60.7       87.6      1.48  3.71                                 12    261     57.6       87.2      1.60  3.63                                 13    279     63.4       86.5      1.89  3.78                                 14    285     57.1       85.0      2.05  4.11                                 15    306     57.2       86.9      1.80  3.59                                 16    308     63.2       85.1      1.86  4.08                                 ______________________________________                                    

EXAMPLE 2

A catalyst having the same composition as that of Example 1 and asurface area of 5.6 m² /gm is tested. The pressure of the reaction isincreased to 3.46 kg/cm² absolute, which results in a reduction inconversion and selectivity to methacrolein as will be seen in Table II.The space velocity of the feed gas was 3000 hr⁻¹ and the composition ofthe gas was essentially the same as in Example 1, except that 8.5 vol %tertiary butyl alcohol (TBA) was submitted for the isobutylene feed usedin Example 1, with the result that after dehydration the composition ofthe gas was 7 vol % isobutylene, 9.8 vol % oxygen, and 20 vol % steam,with the remainder being nitrogen. The temperature ranged between335°-340° C.

It will be observed from a comparison of Tables I and II that increasingthe pressure of the reaction resulted in an inferior performance, asindicated by the poorer selectivity to the desired product, methacroleinand the increase of by-product, acetic acid and CO/CO₂. Since conversionwas lower in this example, selectivity would be expected to be higherthan that of Table I, if the increased pressure had not had an effect.This inferior performance at higher pressure was found even though thecatalyst of Table II had not been used as long as the catalyst of TableI, which might have suffered some loss in performance with time. It maybe concluded that the oxidation of isobutylene and/or tertiary butylalcohol (they are considered to be equivalent feed stocks) tomethacrolein is sensitive to increases in pressure in this relativelylow range. It will be appreciated that a pressure above atmosphericwould normally be used and that the pressure of 3.46 kg/cm² absoluteused in Example 2 is a more realistic value for industrial applications.

                  TABLE II                                                        ______________________________________                                                       Selectivity, %                                                               TBA        Methacrolein +                                       Test  Time,   Conversion,                                                                              Methacrylic                                                                             Acetic                                                                              CO +                                 No.   hr.     %          Acid      Acid  CO.sub.2                             ______________________________________                                        17    38      46         76.5      6.1   13.2                                 18    54      51         75.8      5.2   13.3                                 19    56      50         76.5      5.4   12.3                                 20    58      46         77.4      5.0   11.4                                 21    60      47         78.3      4.7   10.8                                 22    66      43         77.5      4.4   12.3                                 23    68      46         78.3      4.7   11.1                                 24    80      60         79.3      5.0    9.8                                 25    82      60         77.3      5.5   10.9                                 26    86      50         78.9      4.4   11.0                                 27    92      45         79.7      4.4   10.6                                 28    96      60         76.3      5.2   13.1                                 29    100     61         76.9      6.1   12.1                                 30    104     61         77.7      5.6   11.7                                 31    108     57         79.1      5.5   10.5                                 32    118     51         79.4      5.0   10.4                                 33    122     52         80.5      4.4   10.0                                 34    126     51         79.2      4.9   10.6                                 35    130     50         78.8      4.8   11.1                                 ______________________________________                                    

EXAMPLE 3

Example 2 is repeated except that in making the catalyst, it is heatedto about 600° C. rather than the 380° C. used in Example 2. The surfacearea of the catalyst is found to be 2.4 m² /gm. The feed gas compositionwas 5.7 vol. % TBA, 9.8 vol % oxygen, 20% steam, and the remaindernitrogen. It is found that a temperature of 435°-445° C. is required toobtain a conversion of 33-36% and a selectivity to methacrolein plusmethacrylic acid of about 75.5%. The CO+CO₂ selectivity is found to beabout 20%. THus, heating the catalyst to a temperature of 600° C.,instead of the 380° C. of Example 2, results in a significantdeterioration of catalyst performance.

EXAMPLE 4

In 750 cc of water are dissolved 636 grams of the molybdenum salt (NH₄)₆Mo₇ O₂₄.4H₂ O. Then 349 grams of Co(NO₃)₂.6H₂ O are dissolved in 400 ccof water, 363 grams of Fe(NO₃)₃.9H₂ O are dissolved in 400 cc of water,175 grams of Ni(NO₃)₂.6H₂ O are dissolved in 300 cc of water, 40 gramsof Tl NO₃ are dissolved in 400 cc of water, 17.4 grams of CsNo₃ aredissolved in 100 cc of water, 6 grams of KOH are dissolved in 50 cc ofwater, 20.4 grams of SbCl₃ are dissolved in 30 cc of water and 10 cc ofconcentrated HCl, and 145 grams of Bi(NO₃)₂.5H₂ O are dissolved in 100cc H₂ O and 25 cc of concentrated nitric acid. To all the abovesolutions in admixture, 300 grams of 40% colloidal silicon dioxide(Ludox HS 40%, obtained from E. I. DuPont de Nemours and having anaverage particle size of 120 A° and a BET surface area of 232 m² /gm)are added. Sufficient ammonium hydroxide is added to bring the pH of thesolution to a value of 7. Then the solution is evaporated to dryness andprepared as pellets in the manner described in Example 1, except thatthe pellets are activated by heating in air at a rate of 20° C. per hourto about 340° C. and then heated rapidly to 600° C. and held at thattemperature for 2.5 hours. The finished catalyst has atomic ratios ofmolybdenum, cobalt, iron, bismuth, thallium, antimony, silicon, nickel,cesium, and potassium of 12, 4, 3, 1, 0.5, 0.3, 6.6, 2, 0.3 and 0.3,respectively, based on the composition of the original solutions. Duringactivation, the surface area is reduced from about 23 m² /gm to 5.1 m²/gm.

The catalyst was tested under the conditions of Example 3, except that atemperature of only about 335° C. was needed to obtain the superiorresults shown in Table III. The catalyst is superior to the results ofExample 2 and also of Example 1, which was carried out at the morefavorable pressure of one atmosphere.

                  TABLE III                                                       ______________________________________                                                       Selectivity, %                                                               TBA        Methacrolein +                                       Test  Time,   Conversion,                                                                              Methacrylic                                                                             Acetic                                                                              CO +                                 No.   hr.     %          Acid      Acid  CO.sub.2                             ______________________________________                                        36    12      67         84.7      2.4   6.3                                  37    18      70         83.9      2.3   7.5                                  38    22      70         84.2      2.2   7.1                                  39    26      72         84.2      3.3   5.0                                  40    34      70         84.9      2.2   6.6                                  41    38      70         85.2      2.4   6.4                                  42    60      71         83.8      2.7   6.2                                  43    100     68         84.2      2.1   7.6                                  44    2000    68         84.4      2.4   6.5                                  ______________________________________                                    

It can be seen that the catalyst of Example 1 with added nickel, silica,cesium, and potassium has superior performance compared to the prior artcatalyst of Example 1, but under the more severe conditions of Example3.

EXAMPLE 5

Similar results are shown in the following Table IV in which a catalysthaving the same composition as Example 4 is prepared, except that thesilicon content is raised from an atomic content of 6.6 to 12. Thesurface area of the catalyst was reduced from about 23 m² /gm to 7.8 m²/gm by heating to 600° C. during preparation of the catalyst. Incontrast to the previous examples, the feed composition, pressure, andspace velocity were varied during the test run.

EXAMPLE 6

The effect of nickel on the catalyst of the invention is shown in thefollowing Table V in which the catalyst composition of Example 4, butexcluding the nickel content, is tested under the same conditions as inExample 4.

                  TABLE V                                                         ______________________________________                                                       Selectivity, %                                                                      TBA   Methacrolein +                                     Test Time,   Temp,   Conv. Methacrylic                                                                             Acetic                                                                              CO +                               No.  hr.     °C.                                                                            %     Acid      Acid  CO.sub.2                           ______________________________________                                        60    9      368     65    82.5      3.1   9                                  61   11      368     66    83.3      3.3   8                                  62   13      366     64    83.6      2.9   8.9                                63   19      372     68    80.9      3.2   11                                 ______________________________________                                    

                                      TABLE IV                                    __________________________________________________________________________           Feed Gas                   Selectivity, %                                     Composition       Space                                                                              iC.sub.4                                                                          Methacrolein +                              Test                                                                             Time,                                                                             Vol. %   Pressure                                                                           Temp.                                                                             Velocity                                                                           Conv.                                                                             Methacrylic                                 No.                                                                              hr. iC.sub.4                                                                         O.sub.2                                                                          H.sub.2 O                                                                        Atm. °C.                                                                        hr.sup.-1                                                                          %   Acid                                        __________________________________________________________________________    45 6   5.7                                                                              16 20 2.36 364 1000 72.6                                                                              81.3                                        46 9   5.7                                                                              16 20 2.36 379 1000 74.5                                                                              79.4                                        47 24  5.7                                                                              9  16 3.38 362 3000 46.7                                                                              85.6                                        48 26  5.7                                                                              9  16 3.38 362 3000 50.8                                                                              83.4                                        49 35  5.7                                                                              9  16 3.38 341 3000 39.4                                                                              85.1                                        50 48  5.7                                                                              9  16 3.38 355 3000 45.5                                                                              84.9                                        51 51  5.7                                                                              9  16 3.38 356 3000 46.1                                                                              84.1                                        52 60  5.7                                                                              9  16 3.38 365 3000 49.9                                                                              84.1                                        53 79  5.7                                                                              9  16 3.38 360 3000 50.3                                                                              86.0                                        54 81  5.7                                                                              9  16 3.38 365 3000 50.4                                                                              84.4                                        55 96  5.7                                                                              9  16 3.38 379 3000 53.9                                                                              85.1                                        56 116 7  16 15 2.36 380 2250 49.3                                                                              83.4                                        57 119 7  16 15 2.36 380 2250 51.7                                                                              83.4                                        58 122 7  16 15 2.36 388 2250 54.9                                                                              82.4                                        59 128 7  16 15 2.36 388 2250 57.1                                                                              81.6                                        __________________________________________________________________________

Comparing Tables III and V, it can be seen that the conversion oftertiary butyl alcohol is lower when the catalyst lacks nickel, asindicated both directly by measurement and indirectly by the temperaturerequired for the reaction. The surface area of the catalyst is 4.8 m²/gm.

EXAMPLE 7

A catalyst is prepared according to Example 4 except that potassium andcesium were replaced by calcium and 52.8 grams of Ca(C₂ H₃ O₂).H₂ O isdissolved in 200 cc of water and added to the solution to providecalcium in a catalyst having the following composition (based on theoriginal solutions):

    Mo.sub.12 Co.sub.4 Fe.sub.3 Bi.sub.1 Tl.sub.0.5 Sb.sub.0.3 Si.sub.6.6 Ni.sub.2 Ca.sub.1 O.sub.j

The catalyst is heated to about 600° C. for 3 hours during thecalcination which caused the surface area to be reduced from about 20 m²/gm to 5 m² /gm. The catalyst was tested with a feed composition of 7vol % isobutylene, 15 vol % steam, 16 vol % oxygen, and the remaindernitrogen and a pressure of 2.44 kg/cm² absolute and a space velocity ofabout 2250 hr⁻¹ with the following results.

                  TABLE VI                                                        ______________________________________                                                       Selectivity, %                                                                      iC.sub.4                                                                            Methacrolein +                                     Test Time,   Temp,   Conv. Methacrylic                                                                             Acetic                                                                              CO +                               No.  hr.     °C.                                                                            %     Acid      Acid  CO.sub.2                           ______________________________________                                        64    9      345     66    78.2      3.7   10.7                               65   33      371     75    80.8      3.7   10.6                               66   42      379     84    79.7      5.2   11.2                               67   63      379     87    80.7      3     12.6                               68   91      351     83    79.6      4     11.8                               ______________________________________                                    

EXAMPLE 8

A catalyst is prepared according to Example 4 except that 124 grams ofLa(NO₃)₃.5H₂ O is dissolved in 300 cc of water and added to the solutionto provide lanthanum in a catalyst having the following composition(based on the original solutions):

    Mo.sub.12 Co.sub.4 Fe.sub.3 Bi.sub.1 Tl.sub.0.5 Sb.sub.0.3 Si.sub.6.6 Ni.sub.2 La.sub.1 Cs.sub.0.3 K.sub.0.3 O.sub.j.

EXAMPLE 9

A catalyst prepared according to Example 4 except that 76.2 grams of(NH₄)₆ W₇ O₂₄.H₂ O is dissolved in 300 cc of water and added to thesolution to provide tungsten in a catalyst having the followingcomposition (based on the original solutions):

    Mo.sub.12 Co.sub.4 Fe.sub.3 Bi.sub.1 Tl.sub.0.5 Sb.sub.0.3 Si.sub.6.6 Ni.sub.2 W.sub.1 Cs.sub.0.3 K.sub.0.3 O.sub.j.

In addition to the effect of the revised catalyst composition, it isbelieved to be important to maintain the catalyst surface area within arelatively narrow range, broadly 0.5-10 m² /gm and preferably 2-6 m² /gmas measured by the BET method. The surface area is related to the poresize since a particle containing many small pores will have a largesurface area, and a particle containing only large pores will have arelatively small surface area. Heating the catalyst for a sufficientperiod of time to a temperature of at least 525° C. and preferably above550° C. appears to have the effect of eliminating the smaller pores andthus reducing the surface area. Although calcination of the catalystbefore use at about 600° C. is preferred, calcination at somewhat lowertemperatures, at least about 525° C., can be carried out if the surfacearea of the finished catalyst is below about 10 m² /gm and preferablybelow about 6 m² /gm, as will be seen from the following Example 10.

EXAMPLE 10

A catalyst is prepared according to Example 4 to produce a catalysthaving the following composition (based on the original solutions):

    Mo.sub.12 Co.sub.4 Fe.sub.3 Bi.sub.1 Tl.sub.0.5 Sb.sub.0.3 Si.sub.6.6 Ni.sub.2 Cs.sub.0.3 K.sub.0.3 O.sub.j.

The catalyst is heated to about 550° C. for three hours duringcalcination which produced a surface area of 9.6 m² /gm the catalyst istested with a feed composition of 5.4 vol % isobutylene, 9.8 vol %oxygen, 16 vol % steam, and the remainder nitrogen and a pressure of 3.4kg/cm² absolute, a temperature about 335° C., and a space velocity ofabout 3000 hr⁻¹ with the following results.

                  TABLE VII                                                       ______________________________________                                                      iC.sub.4 ═                                                                           Methacrolein +                                       Test  Time,   Conversion,                                                                              Methacrylic                                                                             Acetic                                                                              CO +                                 No.   hr.     %          Acid      Acid  CO.sub.2                             ______________________________________                                        69     8      74.6       82.15     2.58  8.01                                 70    10      73.5       82.25     2.50  8.07                                 71    12      74.2       82.73     2.54  7.83                                 72    14      74.5       82.64     2.30  8.24                                 73    26      68.5       82.5      2.51  8.2                                  ______________________________________                                    

EXAMPLE 11

A catalyst having the composition Mo₁₂ Co₄ Fe₃ Bi₁ Tl₀.5 Sb₀.3 Si₆.6 Ni₂Cs₀.3 K₀.3 O_(j), is measured to have a total surface area of 23 m² /gmafter calcination at temperatures up to 380° C. The pore volume ismeasured by the mercury porisimeter method to be 0.3 cc/gm and the poredistribution is measured by the same method to be such that 70% of thecatalyst internal area belongs to pores 100 A° diameter and larger and30% of the internal area belongs to pores smaller than 100 A°. Themedian pore diameter is 1600 A°.

A catalyst was prepared identically to that described above except thatit was calcined at 600° C. for three hours in air. The pore volumeremains 0.3 cc/gm, but the total surface area is found to be 6.24 m² /gmand 97% of the internal area belongs to pores 100 A° diameter and largerand only 3% of the internal area belongs to pores smaller than 100 A°diameter. The median diameter is 3,660 A°.

As indicated by Example 11, one effect of heating the catalyst to higherthan normal temperatures is to reduce the surface area by eliminatingthe pores having a diameter smaller than about 100 A°, which has theeffect of increasing the average pore diameter. Other effects may alsobe important.

What is claimed is:
 1. A catalyst composition suitable for thevapor-phase oxidation of isobutylene and/or tertiary butyl alcohol toproduce methacrolein consisting essentially of the oxides of molybdenum,cobalt, iron, bismuth, thallium, antimony, silicon, nickel, and a memberof the group consisting of the alkali metals, the alkaline earth metals,the rare earth metals including lanthanum, tungsten, and mixturesthereof and having a BET surface area between about 0.5 and about 10square meters per gram of catalyst.
 2. A catalyst composition as definedin claim 1 which has been calcined in air at a temperature of at leastabout 525° C. for a period of time sufficient to reduce the BET surfacearea to the defined values.
 3. A catalyst composition as defined inclaim 1, having the formula Mo_(a) Co_(b) Fe_(e) Bi_(d) Tl_(e) Sb_(f)Si_(g) Ni_(h) X_(i) O_(j), wherein X is one or more members of saidgroup of alkali metals, alkaline earth metals, rare earth metalsincluding lanthanum, tungsten, and mixtures thereof, and where: a=12;b=0.2-8; c=0.05-5; d=0.2-4; e=0.01-5; f=0.01-5; g=1-20; h=0.05-5; i=apositive value up to 4; j is dependent upon the valence and proportionsof the other elements.
 4. A catalyst composition as defined in claim 3wherein the BET surface area is between about 2 and about 6 squaremeters per gram of catalyst and no more than about 3% of the surface ofsaid catalyst is associated with pores having a diameter smaller than100 Angstroms.
 5. A catalyst composition suitable for the vapor-phaseoxidation of isobutylene and/or tertiary butyl alcohol to producemethacrolein containing molybdenum, cobalt, iron, bismuth, thallium,antimony, and silicon wherein the improvement comprises addingcatalytically effective amounts of nickel and, a member of the groupconsisting of alkali metals, the alkaline earth metals, the rare earthmetals including lanthanum, tungsten, and mixtures thereof, andcalcining said catalyst before use in said oxidation at a temperature ofat least 525° C. in air for a sufficient period of time to reduce theBET surface area to the range of about 0.5-10 m² /gm.
 6. A catalystcomposition as defined in claim 5 wherein the BET surface area isbetween about 2 and 6 square meters per gram of catalyst and no morethan about 3% of the surface area of said catalyst is associated withpores having a diameter smaller than 100 Angstroms.
 7. A catalystcomposition as defined in claim 5 having the formula Mo_(a) Co_(b)Fe_(c) Bi_(d) Tl_(e) Sb_(f) Si_(g) Ni_(h) X_(i) O_(j), where X is one ormore members of said group of alkali metals, alkaline earth metals, rareearth metals including lanthanum, and tungsten and where: a=12; b=0.2-8;c=0.05-5; d=0.2-4; e=0.01-5; f=0.01-5; g=1-20; h=0.05-5; i=a positivevalue up to 4; and j is dependent upon the valence and proportions ofthe other elements.